With rapid development of semiconductor manufacturing technology, semiconductor chips are desirable to have high degree of integration such that semiconductor devices may provide faster computing speed, greater data storage capacity and more features. The semiconductor chips having a higher degree of integration may provide smaller critical dimension (CD) of the semiconductor devices.
Three-dimensional integrated circuits (3-D ICs) may be formed by stacking chips together using advanced technology. Various chips with different functions may be stacked into an integrated circuit having a three-dimensional structure. Compared with a two-dimensional (2-D) structured ICs, the stacking technology for the three-dimensional integrated circuits may allow shortened signal transmission path and accelerated operational speed. In short, 3-D IC stacking technology has advantages including higher performance, smaller size, lower power consumption, and other function for semiconductor devices.
Connection methods between three-dimensional integrated circuit chips include metal wire bonding and flip-chip wafer bonding. Compared with metal wire bonding, the flip-chip wafer bonding has shorter electrical connection path in addition to providing more excellent thermal properties, electrical properties, and smaller structural dimensions. The flip-chip wafer bonding technology is currently, widely used for temporary or permanent bonding between different chips.
The flip-chip wafer bonding technology includes: silicon-silicon direct bonding, silicon-glass electrostatic bonding, and metal-metal bonding. Metal-metal bonding may use pure metal or metal alloy to bond surfaces of two wafers together via intermetallic diffusion, diffusion between metal and wafer, metal molten etc.